\begin{tikzpicture}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(180:1.5){C}
    \tkzDefPoint(0:1.5){D}
    \tkzDefPointOnLine[pos=2/10](D,C)  \tkzGetPoint{P}  % 由 AP=4, PD=2, 得 CP=8
    \tkzDefLine[perpendicular=through P](C,D)  \tkzGetPoint{a}
    \tkzInterLC(P,a)(O,C)  \tkzGetPoints{B}{A}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawPoint(O)
    \tkzDrawSegments(A,B  C,D)
    \tkzMarkRightAngle[size=.2](D,P,A)
    \tkzLabelPoints[below](O)
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[below](B)
    \tkzLabelPoints[left](C)
    \tkzLabelPoints[right](D)
    \tkzLabelPoints[below left](P)
\end{tikzpicture}

